1. Field of the Invention
The present invention relates to vibration motor that generates a drive force by producing elliptical movement in a rod-shaped elastic body, and in particular, it relates to a vibration motor which has a two-phase drive of a longitudinal vibration mode and a bending vibration mode.
2. Description of the Related Art
FIG. 6 is a diagram indicating a conventional linear type vibration motor. With the conventional linear type vibration motor, an excitation transformer 102 is arranged on one edge of a rod-shaped elastic body 101, and a damping transformer 103 is positioned on the other side. Vibrators 102a and 103a are joined to transformers 102 and 103. By applying alternate current from an oscillator 102b to excitation vibrator 102a, rod-shaped elastic body 101 is made to oscillate, and this vibration is a progressive wave propagated on rod-shaped elastic body 101. A moving body 104, which is pressure joined to rod-shaped elastic body 101, is driven by this progressive wave.
Meanwhile, the vibration of rod-shaped elastic body 101 is transmitted to vibrator 103a through damping transformer 103, and the vibration energy is converted to electrical energy by this vibrator 103a. Load 103b connected to this vibrator 103a absorbs the vibrations based on the fact that electrical energy is consumed. The damping transformer 103 prevents the production of standing waves of a mode inherent to rod-shaped elastic body 101 by suppressing the reflection of the end surface of rod-shaped elastic body 101.
The linear type vibration motor shown in FIG. 6 has problems such as only having a moveable range of moving body 104, rod-shaped elastic body 101 must be long, the entire length of rod-shaped elastic body 101 must be made to vibrate, and the motor must be made large scale. In addition, in order to prevent the generation of standing waves of a particular mode, damping transformer 103, for example, is necessary.
To resolve this kind of problem, a variety of self-advancing type vibration motors have been proposed. For example, there is the "asymmetric degeneracy longitudinal L1-bending B4 mode-flat plate motor" which is listed in "222 Piezo Linear Motors for the Purpose of Optical Pickup Movement" of the "Proceedings of the Fifth Electromagnetic Force Dynamics Symposium".
FIG. 7(A) is a front view diagram, FIG. 7(B) is a side view diagram, and FIG. 7(C) is a top view diagram of a conventional example of a heteromorphic degeneracy longitudinal L1-bending B4 mode-flat plate motor.
Elastic body 1 comprises a rectangular wave flat plate shaped base part 1a, and protruding parts 1b and 1c are formed on one surface of base part 1a. Piezoelectric elements 2 and 3 are fixed to the other side of the base part 1a of elastic body 1, and they are elements that generate a longitudinal vibration L1 mode and a bending vibration B4 mode.
Protruding parts 1b and 1c of elastic body 1 are provided on the antinode position of the bending vibration B4 movement which is generated on base part 1a, and are pushed by such relative movement members as guide rails (not shown in the diagram).
However, the motor described above in FIGS. 7(A) through 7(C) has the problem that it can not be optimally controlled because the status of the vibrations of the elastic body 1 can not be detected.